1. Field of the Invention
The present invention relates to an electronic control system of an intake amount for an engine that is used in an engine control unit (ECU) for carrying out an ignition control, a fuel injection control and the like of an automobile engine, particularly in a composite type ECU in which an electronic throttle control function for controlling a throttle valve opening by means of an electric motor is added, and in which safety of the additional function and evacuation operation performances under abnormal state are improved.
2. Background Art
An electronic throttle control system for controlling a throttle valve opening for an intake of an engine in accordance with a depression degree of an accelerator pedal using an electric motor has been widely put into practical use. Recently a wireless type that does not have any accelerator wire has been coming into wide use.
This type of electronic throttle control system is arranged such that when a power supply for the electric motor is interrupted upon occurrence of any abnormality, the throttle valve is automatically returned to a predetermined safe throttle valve opening position by a default mechanism employing a return spring.
The above-described safe throttle valve opening is set to be at a valve opening position a little larger than an idle operating valve opening position. And evacuation operation is carried out in the form of one pedal operation conducting a creep travelling while regulating the depression degree of the brake pedal.
However, in the case that the above-described safe throttle valve opening is small, a problem exists in that even if the brake is released, any sufficient drive force cannot be obtained, and therefore any hill climbing evacuation operation cannot be carried out. On the contrary, in the case that the safe throttle valve opening is excessively large, there arises a dangerous state of having difficulty in stopping the vehicle in spite of sufficiently depressing the brake pedal.
Further, it is necessary to take into consideration such a problem that a default return is not carried out properly due to a mechanical trouble in the throttle valve opening control.
To cope with such problems as described above, a prior art employed a technical improvement as shown in FIGS. 17a to 17d. 
FIG. 17a shows an evacuation operation method in the case that a motor or a throttle valve open/close mechanism is abnormal, and the throttle valve is returned to the valve opening position below a predetermined default position.
In the drawing, reference numeral 1a designates threshold setting means for the upper limit (supremum) vehicle speed, and numeral 1b designates vehicle speed detecting means. Numeral 2a designates threshold setting means for an idle engine speed, and numeral 2b designates engine speed detecting means of the engine. Numerals 3a, 3b designate return detecting switches for the accelerator pedal. Numeral 4 designates supply fuel control means for controlling a fuel injection amount, and numeral 5 designates a fuel injection valve. When the accelerator pedal is returned, the fuel amount is controlled by the supply fuel control means 4 so that the engine speed may be not more than the threshold value set by the threshold value setting means 2a. Thus the drive force of the engine comes to be in a minimum state. Furthermore when the accelerator pedal is depressed, the fuel amount is controlled by the supply fuel control means 4 so that the vehicle speed may be not more than the threshold value set by the threshold value setting means 1a. 
However, in this prior art, the throttle valve opening is so small that a sufficient vehicle speed cannot be obtained. To the utmost, it is a driving function at a lowermost limit intending to get out of the trouble spot.
The operation control system shown in FIG. 17a is disclosed in the Japanese Patent Publication (unexamined) No. 97087/2000, titled xe2x80x9cThrottle Valve Control Systemxe2x80x9d (Reference 1). This operation control system is suitably applied when the throttle valve opening at the time of stopping the motor is not more than the default opening. During the accelerator pedal being depressed, the engine speed is not limited and therefore this operation method is suitable for a low-speed hill climbing evacuation operation.
As a further characteristic of this prior control system a two-pedal operation system is employed based on the generally accepted conception that acceleration is to be conducted by means of the accelerator pedal, and the deceleration is to be conducted by means of the brake pedal. However, a most serious problem exists in this type of control system that the accelerator pedal cannot perform a function of proportionally increasing or decreasing the vehicle speed or engine speed.
The operation control system shown FIG. 17b is applied to the above-described Example 1, in which under the abnormal state that the throttle valve opening at the time of stopping the motor is not less than the default opening. In this operation system, the supply fuel control means 4 is controlled in such a manner that the engine speed may be not more than the threshold value set by the upper limit engine speed setting means 2c. 
On the other hand, in the region of a low engine speed, output torque of the engine increases in proportion to the engine speed, and proportional constant thereof increases or decreases substantially in proportion to the throttle valve opening.
Accordingly, a problem exists in this type of control system that even if the upper limit engine speed is regulated so as to be not more than the threshold value, the actual throttle valve opening is indefinite, and that engine drive torque is varied depending upon the valve opening. Further there is a possibility that braking by means of the brake pedal becomes difficult in the case of large valve opening.
Therefore, supposing that the upper limit threshold engine speed might be lowered, any sufficient drive force cannot be obtained. In particular, a problem exists in that the hill climbing evacuation travelling cannot be carried out at all in the case of small valve opening.
The operation system shown in FIG. 17c is disclosed, besides in the foregoing Example 1, in the Japanese Patent Publication (unexamined) No. 176141/1990 titled xe2x80x9cControl System for Internal Combustion Enginexe2x80x9d (Example 2), the Japanese Patent Publication (unexamined) No. 141389/1999 titled xe2x80x9cThrottle Control System of Internal Combustion Enginexe2x80x9d (Example 3), the Japanese Patent Publication (unexamined) No. 229301/1994 titled xe2x80x9cOutput Control System of Internal Combustion Enginexe2x80x9d (Example 4), etc. This operation is a typical evacuation operation method in the case that the motor or the throttle valve open/close mechanism is in the normal state.
In the drawing, numeral 6a designates an accelerator position sensor (referred to as APS) that detects the degree of the depression of the accelerator pedal. Numeral 7 designates target throttle valve opening setting means in response to the output detected by the APS. Numeral 6b designates a throttle position sensor (referred to as TPS) that detects the throttle valve opening in cooperation with an open/close controlling motor 9 for the throttle valve. Numeral 8 designates PID control means for controlling the above-described motor 9 so that the target throttle valve opening set by the setting means 7 may coincide with an actual valve opening by means of the throttle position sensor 6b. The arrangement described above is the same as that under the normal operation.
However, in the case of occurring any other abnormality except in the motor or the drive mechanism, the target throttle valve opening set by the setting means 7 is a restrained value as compared with that under the normal operation.
In the case of the above-described Example 2, there is proposed abnormality detecting means for detecting an abnormality in output voltage level, abnormality of sudden change, abnormality in relative comparison, etc. in the accelerator position sensor and the throttle position sensor which are provided in the form of dual system. Upon occurring any of these abnormalities, the target throttle valve opening is suppressed.
In the case of the above-described Example 3, acceleration suppression means 10 is used after the setting means 7. As a characteristic thereof, this operation is controlled such that the actual throttle valve opening increases gradually even if the target valve opening increases sharply, and such that the actual throttle opening comes to be small upon decreasing the target valve opening.
In this type, the evacuation operation is a usual two-pedal operation, which is characterized in that there is no uncomfortable feeling. However, a problem exits in that drive torque of the engine becomes decreased due to the target valve opening being suppressed, whereby any sufficient hill climbing performance cannot be obtained.
In particular, a problem exits in that any technique of identifying non-defective, wherein if one of the abnormality determination means such as APS or TPS is in failure, the other one is automatically selected, is not employed. A further problem exits in that the suppression of the target valve opening is not carried out in a rational and quantitative manner.
FIG. 17d shows a method of the evacuation operation in the case that the motor or the throttle valve open/close mechanism is abnormal, while the accelerator position sensor is effective. This operation method is shown in the above-described Example 4.
In the drawing, numeral 2d designates operation threshold setting means for variably setting the upper limit engine speed substantially in proportion to the output detected by the accelerator position sensor 6a. The supply fuel control means 4 controls the fuel injection valve 5 such that the actual engine speed may be equal to the threshold value.
A characteristic of the system shown in Example 4 is that in the case of an actuator system being in the normal state, the evacuation operation as shown in FIG. 17c is performed. On the other hand, in the case of the actuator system being in the abnormal state, the evacuation operation as shown in FIG. 17d is performed. In either case, the two-pedal operation, which is comfortable for the driver, is carried out.
In this drawing, however, what sort of evacuation operation is to be carried out in the case that the accelerator position sensor is in failure, is not shown. Particularly, supposing that the output voltage detected by the accelerator position sensor might be excessively large when the accelerator pedal is returned to its position, there may arise a dangerous state difficult to stop by means of the brake pedal.
In the Japanese Patent Publication (unexamined) No. 137206/1994 titled xe2x80x9cElectronic Control System for Enginexe2x80x9d (Example 5), a still further concept is proposed. In this proposal, operation of the target valve opening is carried out by means of both CPU 1 for the fuel control and CPU 2 for the valve opening control. The target valve opening of the CPU 1 is used as a substitution in the case of occurring an abnormality such as sum check error in the target valve opening signal of the CPU 2.
In addition, also in the case of the foregoing Example 5, it is described that the evacuation operation is carried out in the following manner. That is, when the CPU 2 for the valve opening control or the actuator is in abnormal state, such evacuation operation as shown in FIG. 17d is performed if the accelerator position sensor is normal. On the other hand, such evacuation operation as shown in FIG. 17b is performed if one of a pair of accelerator position sensors is abnormal.
(1) Description about Problems Incidental to the Prior Arts
In the prior arts as discussed above, the abnormality detecting means for the added electronic throttle control system and the evacuation operation method in accordance with the abnormality detecting means are not systematically associated. Therefore, a problem exits in that even when the actuator system and the accelerator position sensor are normal, an engine torque generated at the time of evacuation operation is restrained, eventually resulting in lowering of a climbing performance. Another problem exists in that when the actuator system and the accelerator position sensor are abnormal, braking by means of the brake pedal becomes difficult or any sufficient drive force is not secured.
Furthermore, when it is determined that the actuator system is abnormal while the accelerator position sensor is normal, a problem exits in that braking by means of the brake pedal becomes difficult as long as there is any abnormality in the accelerator position sensor.
A first object of the present invention is to systematically extract any abnormality in sensor system, control system and actuator system to divide them into a serious abnormality and a slight abnormality, and then provide various evacuation operation means corresponding to the abnormality state.
A second object of the invention is to make it possible to perform a two-pedal evacuation operation safely in the same feeling as in normal operation using an accelerator pedal and a brake pedal, even when there is any abnormality in the actuator system or throttle position sensor so long as the control system and accelerator position sensor are regarded as being normal.
A third object of the invention is to make it possible to perform a one-pedal evacuation operation by means of the brake pedal safely, even when there is no accelerator position sensor regarded as being non-defective and, moreover, any default return abnormality of the actuator is generated.
To accomplish the foregoing objects, an engine control system according to the invention includes: motor drive control means that is power fed via a power supply switch from a vehicle-mounted battery and controls an open/close driving motor of a throttle valve for an intake of the engine in response to an output from an accelerator position sensor for detecting a degree of a depression of an accelerator pedal and an output from a throttle position sensor for detecting a throttle valve opening; fuel injection control means for the engine; and engine speed or vehicle speed detecting means; and includes a microprocessor (CPU);
the engine control system including multi-stage abnormality detecting means, multi-stage evacuation operation means, and evacuation operation mode selection means;
wherein the abnormality detecting means is multi-stage abnormality detecting means that regularly monitors operations of sensor system, control system and actuator system relating to a throttle valve control, and identifies and detects slight abnormality and serious abnormality depending on whether or not at least control of the actuator is possible;
the evacuation operation means is multi-stage evacuation operation means that responds to any abnormality result detected by the multi-stage abnormality detecting means, and comprises at least slight abnormality evacuation operation means and serious abnormality evacuation operation means; and
the evacuation operation mode selection means is means for selecting one of the multi-stage evacuation operation means so that shift from a normal operation when the slight abnormality or serious abnormality is not generated, to a side of getting worse in abnormality degree toward the slight abnormality evacuation operation or the serious abnormality evacuation operation may be possible, while shift to a return side in the abnormality degree may be impossible without interrupting the power supply switch.
As described above, in the engine control system according to the invention, one of the multi-stage operation means in response to multi-stage degrees of abnormality, i.e., serious abnormality, slight abnormality and the normality, can be selected and operated. Furthermore, in the case that the abnormality degree is changed, the shift of the operation means toward the side of getting worse the abnormality degree is possible, while the shift to the side of restoring the abnormality degree is impossible without interrupting the power supply switch. As a result of such arrangement, an advantage is obtained such that safe driving can be done, and there is no confusion in the driving operation.